1. Field of the Invention
This invention relates to an illumination optical system that splits light from a light source into multiple light beams, and superimposes the multiple light beams on a common illumination area. The invention also relates to a projector which comprises the illumination optical system and which can project images on a screen with a uniform brightness.
2. Description of the Related Art
In a projector, illumination light from an illumination optical system is projected onto light modulators called light valves. The light valves modulate the light in accordance with the image information to be displayed, and the modulated light is projected onto a screen to display the images.
A projector should display the images at a uniform brightness. Generally, however, the intensity of the light is at its highest near the axis of the light source, and declines as the distance from the axis increases. If this light is used without modification as the illumination light, the brightness of the projected images will be uneven. To resolve this problem, in the prior art integrator optical systems are used to ensure uniform illumination of the light modulators comprising the illumination area.
Generally, an integrator optical system splits the light from the light source into multiple light beams, which are then superimposed on the illumination area to achieve uniformity of the illumination.
The ideal light source for an illumination optical system is a point light source, but this is difficult to achieve. In the process of splitting the source light into multiple light beams and superimposing the beams onto the illumination area, an integrator optical system may degrade the efficiency with which light from the light source is utilized.
Images displayed by a projector should be as bright as possible. To achieve this high brightness, ideally the illumination optical system used is one that maximizes the light utilization efficiency.
There is another problem about an integrator optical system that it is difficult to manufacture an array of small lenses of the beam-splitting optical system included in the integrator system with good precision.
Accordingly an object of the invention is to increase light utilization efficiency in an illumination optical system. Another object is to provide a technology that enables the lens array of the beam-splitting optical system to be readily manufactured. Still another object is to provide a projector that enables brighter, more uniform projection images.
In order to attain at least part of the above and other related objects of the present invention, there is provided an illumination system. The illumination system comprises: a light source; a first lens array of small lenses for dividing light from the light source into a plurality of light beams; and a second lens array of small lenses corresponding to the small lenses of the first lens array. The second lens array is located near where the plurality of light beams from the first lens array are converged. Each small lens of the second lens array has an outer shape of a non-rectangular polygon which is related to a profile of the light converged by a corresponding small lens of the first lens array.
Each of the multiple light beams emanating from the small lenses of the first lens array has to fall incident on the associated lens of the second lens array to enable the light to be used effectively for illumination.
The second lens array is comprised of small lenses that are polygonal in shape but not truly rectangular or square, so that they correspond to the shape of the multiple light beams converged by the small lenses of the first lens array. This makes it possible to prevent the multiple beams exiting the small lenses of the first lens array from impinging on small lenses of the second lens array located adjacent to the target small lens. This improves the illumination light utilization efficiency.
According to another aspect of the invention, the second lens array has a flat portion provided between the columns of the small lenses. In this case the second lens array may not have an outer shape of a non-rectangular polygon related to a profile of the light converged by a corresponding small lens of the first lens array.
Since the columns of small lenses of the second lens array are separated by the flat portion, these small lens columns are not in direct mutual contact. Thus the second lens array can be manufactured with good precision more easily than a lens array in which all small lenses are in direct contact with each other.
In the above illumination system, when two reference axes perpendicular to each other are defined to pass through a center of the second lens array, at least some segmentation lines used to segment the second lens array into the plurality of small lenses may have an angle of inclination to the reference axes such that the angle of the inclination increases with an increase in distance from the reference axes.
This configuration enables the small lenses of the second lens array to be shaped to match the inclined profile of the multiple light beams.
The present invention is also directed to a projector comprises: an illumination system having the above configuration; a light modulator that modulates incident light from the illumination system in accordance with image information; and a projection optical system that projects the modulated light.
Since the illumination system of the invention has an integrator optical system including first and second lens arrays, it is possible to obtain light of uniform brightness and color even if there is a major bias in the sectional intensity distribution of the light emitted by the light source. Therefore, it is possible to obtain projection images that exhibit uniform brightness and color across the entire projection plane.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.